Galeruca tanaceti (Linnaeus, 1758)

Although widely distributed throughout England and Wales including the Isle of Wight, Anglesey and Man there are large areas where it appears to be absent eg most west country records are coastal, Welsh records are mostly from the west and much of Lancashire and Northumberland are without records. The southeast, especially south of London, is rich in records although it may have declined over parts of its range (Cox). There are scattered, mostly western, records from Scotland north to Easter Ross. Typical habitat is unmaintained open grassland in a wide range of situations, and the adults occur between June and October, occasionally earlier or later and sometimes they overwinter. They may be found by sweeping although observation is an effective method as adults often sit on high grass stems, in this way copulating pairs are easily found. They generally occur in small numbers over a wide area but we have also found them in large aggregations; during the 1980's they occured on rough grass areas on Harefield Place golf course near Uxbridge (Middx) in groups of many hundreds, the majority of which were mating, and these groups persisted for several weeks. Locally they occur on the drier areas of Common moor but here we have only found them at low density. Adults are known to aestivate in grass tussocks between June and August (Siew, 1966) and during this time we have found numerous specimens crowded into a hollow log lying exposed on the moor (June, July 2006) and also under stones and amoong dry matted grass, at this time adults were occasionally found active during the evening when the temperature dropped. Both adults and larvae are widely polyphagous, adults producing holes in leaves and larvae feeding on exposed surfaces. Known hosts include Tansey (Tanacetum vulgare), Yarrow (Achillea millefolium), Knapweed (Centaurea nigra), Colt's foot (Tussilago), Silverweed (Potentilla auserina), Cuckoo flower (Cardamine pratensis), charlock (Sinapis arvensis), Devil's-bit scabious (Succisa pratensis), Small scabious (Scabiosa columbaria), creeping thistle (Cirsium arvensis), and various speedwells (Veronica spp.). Eggs are laid during September or October in groups within oothecae attached to grass stems and winter is passed in this stage. Larvae emerge towards the end of April and during May and become fully grown around the first half of June. Pupation occurs during late May or June and adults appear between min June and August, persisting until October.

A large and distinctive species, instantly recognisable in the field, entirely black or with the second antennal segment to some extent pale, convex and oval in outline; broadest behind middle of elytra. The only possible confusion is with our other species of the genus, G.laticollis (Sahl), of similar size but here the pronotum and elytra are pale (described by Joy as yellow) and the basal antennal segments are brown. A rare species of coppices and fens with only a few records from southern England.

6-12mm (Joy). Entire upper surface coarsely and densely punctured, that on head and pronotum a little denser than on elytra, cuticle between punctures shiny but the overall appearance is somewhat dull due to the punctures. Eyes relatively small, entire and moderately convex. Head closely punctured, vertex with a longitudinal furrow to clypeus. Antennal insertions closer together than the length of the basal segment. Segments one and three longer than two. Pronotum transverse, parallel or nearly so in basal two thirds then narrowed to obtuse front angles. Lateral margins bordered, deeply so towards front angles. Hind angles obtuse, basal margin irregular and unbordered. Surface roughly sculptured, puncturation dense but uneven so that there may be shiny areas. Elytra puncturation random although there is a tendency towards rows near the suture and they are longitudinally confluent towards the side margins, so much so that they may form furrows. Side margin explanate; widest behind prominent shoulders and narrowed towards apical curvature. Apices separately rounded. Legs entirely black, relatively long and slender. Hind femora not noticeably broader than mid femora. Tibia broadened towards apex, outer edge gently curved, without spines or teeth and covered with dense, short black pubescence. Each claw with a long tooth on inner side.

Description from 6 Watford specimens at X20